1. Field of the Invention
The present invention relates to a continuous damping control shock absorber of a dual solenoid valve structure for preventing a reduction in a compression damping force generated when two solenoid valves are applied, and more particularly, to a continuous damping control shock absorber of a dual solenoid valve structure in which a separator tube for interworking prevention is configured such that a fluid discharged from a rebound solenoid valve flows into not a low-pressure reservoir chamber but a high-pressure compression chamber during a compression stroke, thereby preventing a reduction in a compression damping force, which is caused when a passage of the rebound solenoid valve is arbitrarily opened during the compression stroke.
2. Description of the Related Art
A conventional continuous damping control shock absorber of a dual solenoid valve structure will be described briefly with reference to the accompanying drawings.
FIG. 1 is a longitudinal sectional view illustrating a conventional continuous damping control shock absorber of a dual solenoid valve structure, and FIG. 2 is an enlarged view illustrating main parts of FIG. 1.
As illustrated in FIGS. 1 and 2, the conventional continuous damping control shock absorber of the dual solenoid valve structure includes a base shell 11, and an inner tube 13 which is installed inside the base shell 11 and in which a piston rod 12 is movably installed in a length direction.
A rod guide 14 and a body valve 15 are installed in an upper portion and a lower portion of the inner tube 13 and the base shell 11, respectively.
In the inside of the inner tube 13, a piston valve 16 having an oil passage 16a is connected to one end of the piston rod 12, and the piston valve 16 partitions the internal space of the inner tube 13 into a rebound chamber 17 and a compression chamber 18.
A top cap 21 and a base cap 22 are installed in an upper portion and a lower portion of the base shell 11, respectively.
A rebound separator tube 23 and a compression separator tube 24 are installed in an upper portion and a lower portion between the inner tube 13 and the base shell 11, respectively.
The rebound separator tube 23 and the compression separator tube 24 form a reservoir chamber 25 that compensates for a change in the internal volumes of the rebound chamber 17 and the compression chamber 18 according to a reciprocating motion of the piston rod 12 in the inside of the base shell 11.
In order to vary a damping force, a rebound solenoid valve 30 and a compression solenoid valve 40 serving as damping force variable valves are installed at one side and the other side of the base shell 11, respectively.
During a rebound stroke, the rebound separator tube 23 serves to circulate a fluid of the rebound chamber 17 through the rebound solenoid valve 30 and guide the fluid to the reservoir chamber 25. During a compression stroke, the rebound separator tube 23 serves to circulate the fluid through the rebound solenoid valve 30 and guide the fluid of the reservoir chamber 25 again to the rebound chamber 17.
An inner hole 13a is formed in an upper portion of the inner tube 13 to communicate with a chamber C1, that is, a space formed between the rebound chamber 17 and the rebound separator tube 23.
An inner hole 13b is formed in a lower portion of the inner tube 13 to communicate with a chamber C2, that is, a space formed between the compression chamber 18 and the compression separator tube 24.
The rebound solenoid valve 30 is connected to the rebound chamber 17 through the inner hole 13a, and the compression solenoid valve 40 is connected to the compression chamber 18 through the inner hole 13b. 
During the compression stroke, the compression separator tube 24 circulates the fluid of the compression chamber 18 through the compression solenoid valve 40 and guides the fluid to the reservoir chamber 25.
Due to the rebound separator tube 23, the inside of the base shell 11 is partitioned into a high-pressure chamber PH connected to the rebound chamber 17, and a low-pressure chamber PL serving as the reservoir chamber 25.
Due to the compression separator tube 24, the inside of the base shell 11 is partitioned into a high-pressure chamber PH connected to the compression chamber 18, and a low-pressure chamber PL serving as the reservoir chamber 26.
The rebound and compression high-pressure chambers PH are connected to the rebound chamber 17 and the compression chamber 18 through the inner holes 13a and 13b of the inner tube 13, respectively.
The low-pressure chamber PL of the compression solenoid valve 40 is connected to a passage of the body valve 15 through a lower passage 32 formed between the body valve 15 and the base shell 11.
The operation of the conventional continuous damping control shock absorber of the dual solenoid valve structure as configured above will be described below.
During the compression stroke, when the piston rod 12 moves downward, the fluid (oil) of the compression chamber 18 is compressed, and the inside of the compression chamber 18 becomes high-pressure. Therefore, a part of the fluid existing in the compression chamber 18 circulates through the compression solenoid valve 40 via the inner hole 13b and moves to the low-pressure reservoir chamber 25, and other fluid is introduced into the rebound chamber 17 through the oil passage 16a. 
During the rebound stroke, when the piston rod 12 moves upward, the fluid (oil) of the rebound chamber 17 is compressed, and the inside of the rebound chamber 17 becomes high-pressure. Therefore, a part of the fluid existing in the rebound chamber 17 circulates through the rebound solenoid valve 30 via the inner hole 13a, and other fluid is introduced into the compression chamber 18 through the oil passage 16b. 
A damping force is varied when the fluid is circulated through a series of procedures while undergoing the compression stroke and the rebound stroke.
However, in the conventional continuous damping control shock absorber of the dual solenoid valve structure, the fluid of the compression chamber 18 is bypassed to the rebound chamber 17 through the oil passage 16a of the piston valve 16 during the compression stroke. At this time, the passage of the rebound solenoid valve 30 connected to the reservoir chamber 25 being relatively lower pressure than the rebound chamber 17 is arbitrarily opened. Therefore, since a damping force interworks with the rebound solenoid valve 30 during the compression stroke, the independence of the compression solenoid valve 40 is deteriorated.
In order to solve this problem, as described above, there has been proposed a structure that increases oil passage intake stiffness of the piston valve to prevent the fluid of the high-pressure compression chamber 18 from flowing into the low-pressure rebound chamber 17 during the compression stroke. However, this structure has a problem that lag phenomenon occurs at the time of the change from the compression stroke to the rebound stroke due to the generation of a negative pressure in the rebound chamber 17. Therefore, there is a need for technologies that can prevent a reduction in a compression damping force by preventing the occurrence of lag phenomenon and independently performing a compression mode and a rebound mode without interworking (or interference).